This invention relates to a photoelectric transducer and a solid-state image sensing device using the photoelectric transducer, and more particularly to, a solid-state image sensing device in which smear or crosstalk is reduced.
Typical solid-state image sensing devices using CCD have an interline transfer type two-dimensional CCD solid-state image sensing device and a buried photodiode structure. This is described in, for example, Japanese patent application laid-open No. 57-62557 (1982).
FIG. 1A is a plan view showing an interline transfer type two-dimensional CCD solid-state image sensing device, and FIG. 1B is a cross sectional view cut along the line Fxe2x80x94F in FIG. 1A. In this type of solid-state image sensing device, many photodiodes 1 to generate signal charge by the incidence of light are arrayed. A vertical CCD register 2 is provided for each row of photodiodes. One end of the vertical CCD register 2 is connected to a horizontal CCD register 3, which is connected to an output section 4. The photodiode and the vertical CCD register are formed on a n-well 9 formed on a n-substrate 19. The photodiode is composed of n-region 6 to accumulate signal charge and p+-region the surface. The vertical CCD register is composed of n-well 7 and p-well 8. Between the photodiode and vertical CCD register, there is p+-device separation region 10 or p-region 11 forming a transfer gate. At the upper part of the vertical CCD register, there is provided a gate electrode 12 to apply drive pulse voltage through gate insulator film 13 to the vertical CCD register. Further on the gate electrode 12, light-shielding film 14 is formed sandwiching insulation film 15, and thereby light-generated charge can be prevented from occurring in the vertical CCD register. The whole surface is covered with insulation film 15. The transfer gate is controlled by the gate electrode 12 of vertical CCD register. When positive voltage is applied to the gate electrode, signal charge moves from the n-accumulation region 6 through a channel formed at the transfer gate to the n-well 7.
Here, the end of p+-region 5 adjacent to the transfer gate and on the surface of photodiode is separated from the p-region 11 so as to make signal charge easy to read out from the n-accumulation region 6 to the n-well 7 of vertical CCD register. Thus, the n-region 6 is formed between the p+-region 5 and the p-region 11.
Also, a solid-state image sensing device called frame transfer type other than the interline transfer type is known. The frame transfer type solid-state image sensing device is characterized by its high numerical aperture.
FIG. 2 is a plan view showing a frame transfer type two-dimensional CCD solid-state image sensing device. Different from the interline transfer type, its vertical CCD register functions as both transfer section and light-receiving section. One end of multiple rows of vertical CCD registers 51 is connected to a horizontal CCD register 52, which is connected to output section 53. The occurrence of charge by the incidence of light is performed in the vertical CCD register. In the frame transfer type, since the incidence of light is performed through the gate electrode of vertical CCD register, the sensitivity of the short-wavelength component is not good. Therefore, by providing the vertical CCD register 2 with a window 54 with no gate electrode on its top, the sensitivity of the short-wavelength component can be enhanced.
FIG. 3 is an enlarged view showing the pixel region. Gate electrodes 71 to 74 are periodically disposed in the transfer direction and windows 54 are formed therebetween. The gate electrodes in FIG. 3 are of single layer, but maybe of multiple layers. Light-shielding film 64 to prevent the crosstalk is formed over the gate electrode between pixels. The light-shielding film 64 is connected to the gate electrode by the contact and may be also used as electric interconnection.
FIG. 4A is a schematic plan view showing the surface of substrate below the gate electrode. FIG. 4B is a cross sectional view cut along the line Gxe2x80x94G in FIG. 4A. The n-region 56 is formed below the gate electrode, and p-device separation region 60 is formed below the light-shielding film 64. Also, p-well 59 is formed on n-substrate 69, and n-well 56 is further formed thereon. The n-well 56 is a charge accumulation region for the incidence of light and is also used as a transfer section. In the opening section (window), p+-region 55 is formed on the n-well 56. In the transfer section, a gate electrode 62 to which the drive voltage pulse of CCD is applied through gate insulator film 63 is formed. The p-device separation region 60 is formed between pixels, and light-shielding film 64 is formed sandwiching insulation film 65 thereon. Also, the whole surface is covered with insulation film 65.
In the CCD image sensing device, cell area per one pixel continues to reduce, according to an increase in pixel number and a reduction in device size. In the interline transfer type CCD image sensing device, the distance between the light-receiving section and the transfer section shortens with the reduction of cell area. Therefore, there is a problem that even when the transfer gate is turned off, smear is likely to flow into the transfer section beyond the device separation region. Such smear occurs especially when light with high luminance is supplied. In the buried photodiode structure disclosed in Japanese patent application No. 57-062557 (1982), the smear component due to diffusion of signal charge to generate in the semiconductor substrate becomes an issue. The diffusion-caused smear explained below, referring to the drawings.
FIG. 5 is an enlarged cross sectional view showing the end of p+-region 5 on the side of the p+-device separation region 10 in FIG. 1B. When light is supplied to the image-sensing device, signal charge due to the photoelectric conversion occurs in the surface p+-region 5 and n-accumulation region 6 of the photodiode. Most of the signal charge that occurs in the surface p+-region 5 moves to the n-accumulation region 6. But, part of the light-generated charge occurring at the p+-region 5 near the end of the light-shielding film 14 passes through near the surface of the p+-device separation region 10, then flows into n-well 7 of vertical CCD register to cause a smear.
The same phenomenon is also seen in the case of frame transfer type CCD image-sensing device. In this case, the window incurs crosstalk.
FIG. 6 is an enlarged cross sectional view showing the vicinity of the device separation region of the frame transfer type CCD image-sensing device in FIG. 4B. Signal charge generated in the surface p+-region 55 of the window""s end where light-shielding film 64 opens by the incidence of light passes through the p+-device separation region 60, flowing into then-region 56 for the neighboring pixel to affect the sensitivity of that pixel.
Methods of reducing the diffused smear component have been suggested. For example, Japanese patent application No. 08-130299 (1996) discloses a structure that surface p+-region 25 of photodiode and device separation region 30 are connected by p++-region 38 with high concentration of impurity as shown in FIG. 7A. In FIG. 7A, the composition except the surface p+-region 25 of photodiode and device separation region 30 is the same as that in FIG. 1B. For this composition, the potential distribution of a cross section cut along the line Hxe2x80x94H is shown in FIG. 7B. According to this method, since the potential barrier is formed by built-in voltage by the difference of impurity concentration, the possibility that signal charge comes into a smear component due to the diffusion can be reduced.
However, due to insufficient height of potential barrier, there exists charge to flow into n-well of vertical CCD register. Therefore, it is impossible to reduce the smear to a large extent.
On the other hand, Japanese patent application No. 04-11774 discloses a structure that insulator is buried into device separation region to block the path of signal charge to cause smear. However, in this case, the device characteristic must deteriorate due to the mechanical stress while the smear can be reduced to a large extent.
Accordingly, it is an object of the invention to provide a photoelectric transducer and a solid-state image sensing device that can reduce the smear or crosstalk.
According to the invention, a photoelectric transducer, comprises:
a photodiode that is formed on a second-conductivity-type well and is composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a second-conductivity-type region formed on the first-conductivity-type region;
wherein the second-conductivity-type region except part where the potential of the second-conductivity-type region is grounded is separated from a second-conductivity-type device separation region by the first-conductivity-type region.
According to another aspect of the invention, a solid-state image sensing device, comprises:
a photoelectric transducer comprising a photodiode that is formed on a second-conductivity-type well and is composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a second-conductivity-type region formed on the first-conductivity-type region, wherein the second-conductivity-type region except part where the potential of the second-conductivity-type region is grounded is separated from a second-conductivity-type device separation region by the first-conductivity-type region; and
a signal-charge transfer section or signal line that is connected through a transfer gate to the photodiode;
wherein the second-conductivity-type device separation region is provided in a region except the transfer gate between the photodiode and the signal-charge transfer section or signal line.
According to another aspect of the invention, a solid-state image sensing device, comprises:
(a) plurality of light-receiving units that are arrayed on a second-conductivity-type well and are composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a second-conductivity-type region formed on the first-conductivity-type region, wherein the second-conductivity-type region except part where the potential of the second conductivity-type region is grounded is separated from a second-conductivity-type device separation region that is formed between the light-receiving units by the first-conductivity-type region.
According to another aspect of the invention, a photoelectric transducer, comprises:
a photodiode that is formed on a second-conductivity-type well and is composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a first second-conductivity-type region formed on the first-conductivity-type region;
wherein the first second-conductivity-type region is separated from a second-conductivity-type device separation region and is connected to the second-conductivity-type device separation region at part of the circumference of the first second-conductivity-type region through a second second-conductivity-type region that is formed to be at least partially shallower than the first second-conductivity-type region.
According to another aspect of the invention, a solid-state image sensing device, comprises:
a photodiode that is formed on a second-conductivity-type well and is composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a first second-conductivity-type region formed on the first-conductivity-type region; wherein the first second-conductivity-type region is separated from a second-conductivity-type device separation region and is connected to the second-conductivity-type device separation region at part of the circumference of the first second-conductivity-type region through a second second-conductivity-type region that is formed to be at least partially shallower than the first second-conductivity-type region; and
a signal-charge transfer section or signal line that is connected through a transfer gate to the photodiode;
wherein the second-conductivity-type device separation region is provided in a region except the transfer gate between the photodiode and the signal-charge transfer section or signal line.
According to another aspect of the invention, a solid-state image sensing device, comprises:
a plurality of light-receiving units that are arrayed on a second-conductivity-type well and are composed of a first-conductivity-type region to accumulate signal charge when light is supplied and a first second-conductivity-type region formed on the first-conductivity-type region,
wherein the first second-conductivity-type region is separated from a second-conductivity-type device separation region and is connected to the second-conductivity-type device separation region at part of the circumference of the first second-conductivity-type region through a second second-conductivity-type region that is formed to be at least partially shallower than the first second-conductivity-type region.
For example, when the invention is applied to a CCD solid-state image sensing device, signal charge occurred at p+-region on the surface of photodiode and forwarding to adjacent vertical CCD register or photodiode flows from n-region to separate the p+-region and p+-device separation region into n-accumulation region. Therefore, false signal charge to cause the smear or crosstalk can be prevented from reaching the adjacent vertical CCD register or photodiode. Also, by providing shallow p+-region between the surface p+-region and p+-device separation region, the same effect can be obtained.
Meanwhile, a photoelectric transducer in the invention can be applied not only to a CCD solid-state image sensing device but also to a MOS type solid-state image sensing device. In the MOS type solid-state image sensing device, signal line for transmitting signal charge is provided substituting for the vertical CCD register. Thus, according to the invention, false signal charge from photodiode to signal line can be reduced like the case of CCD solid-state image sensing device.